The apps are advertising that they can do this tho. Many of them are aggressively sponsoring YouTubers who advertise you can basically just wave your phone over the food and it takes away all the “work” from traditional calorie counting apps

Friendly reminder that LLMs don't do math, they guess what number should come next, just like words.

It can probably link the image to the words "a photo of a sandwich on a plate", and interpret the question as "how many calories are in a sandwich" but from there it is just guessing at the syntax of an answer, but not at finding any truth.

It knows sandwiches have calories and those tend to be 3-4 digit numbers, but also all numbers kinda look the same, so what's to say it's not 2, 5, or 12 digits?

Nope, Claude and Gemini both guessed fewer carbs than are in the bread.

What in the picture indicates any form of filling?
What you can see is cheese, there is probably butter too, but those 2 have zero carbohydrates, so adding carbohydrates based on filling would be pure speculation.
There are no carbohydrates to see beyond the bread.
There is no evidence of any filling, as there is zero bulge in the bread.
The answer should be based on what can be seen, with a remark to that effect, and that there possibly could be more if it contains filling that isn't visible.

The AI could ask about a possible filling, instead of just making shit up with zero evidence.